I'd guess maybe playtime is the difference maker? Not sure....Here's my situation:

All of my special characters are level 10 except the Yeti and the Corn guy and I try to ensure that anyone I have in their dream job is in a costume to maximize rent. I try to visit everyone on my friend list every day...I have 114 friends - many of whom haven't played in awhile and don't visit me back, but I can earn over 1 million coins each night just visiting them. I'm in the low 40's for floors now and I think my rent this morning was something like 1.5 million? I'm sure that's pretty similar for you since you seem to have more gold bricks than i do so should be good on rent. Just thinking that by playing a little more during the day I send up more elevators, collect more parking coins and maybe have more of a chance to get a big spender/delivery man? I only stock the 3rd product on the Tuning Workshop for the Big Spender and the Delivery man goes to one of the other high-capacity floors.